Patent GB-884900-A (GB)
Title: Position determining system
IPC: G01S1/02
Filed: 1960-06-20
Abstract: 884,900. Radio navigation; valve pulse delay circuits. SCIENTIFIC SERVICE LABORATORIES Inc. June 20, 1960 [Sept. 11, 1959], No. 21558/60. Classes 40(6) and 40(7). [Also in Group XX] In a system for determining the precise ' location of a station, means determine the approximate range and direction of two spaced targets, means alternately transmits pulse signals towards each of the targets and receives those signals reflected to the station, time measuring means is started simultaneously with the transmission of a pulse and is stopped by a corresponding reflected signal, and the time measurements are registered to fix the station position. The invention is described as applied to the recording of the course of a geophysical surveying ship carrying a conventional azimuth-scanning pulse radar and a known time measuring apparatus, reflecting targets ("red", "green") being provided at known locations on shore. For each target reflections are selected from a region bounded by a bearing sector and a range step, the approximate target range and bearing being known from the radar display. The targets are identified by polarization or otherwise (see below) and the results of several consecutive measurements may be averaged to improve accuracy. The course recorder comprises two arms each of which carries a travelling block controlled by a servomotor the input to which is the voltage difference between the output of a potentiometer driven by the motor and the output of the time measuring means, Fig. 11 (not shown). Synchro-transmitter 62, Fig. 3, is coupled to the aerial driving motor and its output synchronizes receivers 70, 72 via differential 64 coupled to gyro-repeater 66. Plan position indication (P.P.I.) presentation is thus northupwards and the display is utilized to monitor the system operation and to give the manual settings for red and green azimuth selectors 76 and the range control device. Considering the operation of the system for the "red" target the time measuring means is reset immediately following the reaching of the selected azimuth by a pulse to circuit 52, Fig. 4, arising from the change-over of contact 84 from B to A, the arrangement of cam 80 being such that contact 84A is closed when the switch arm is moved out of depression 82 immediately following the aerial direction at the target; signal 106 is fed to relay 104 to make and break switch 108 rapidly and the latter is connected to the resetting circuits 110 of the time measuring means which begins to count on the transmission of the first radar pulse after resetting. Red range-control potentiometer P1 feeds a stop pulse to the time measuring means only when the reflected signals are from targets at substantially the same range as the red target. When the contact 84B closes relay RY1 is energized to connect bias 112 to valve V16 via potentiometer P1 but on change-over to contact 84A the range gate circuits are closed. Range control device 40 is connected to C.R.T. 60, Fig. 3, to provide a bright line extending from the ship to the range set by the potentiometer and the latter is adjusted to the target range by closing switch SW3. Range measurement (red target), Figs. 5 and 6. The transmitted pulse triggers mono-stable multivibrator 114 whose square wave output is applied to a triangular wave forming circuit at valve V1 input. The input network to Schmitt trigger V2 is fed from valve V1 output and from valve V16. Transformer T1 rings when valve V2b goes into saturated conduction and overshoot is prevented by diode D1 so that only the first half cycle appears at the transformer secondary. The transformer output is fed to valve V5 to gate the radar receiver output from amplifier V4 and the echo signal passing through the gate stops the counting operation of time measuring device 38. Bright range arcs on the P.P.1. corresponding to the beginning and end of the gate are provided from cathode follower V3b and transformer T2 respectively, Fig. 5A (not shown); and the latter output may be fed to device 38 to prevent an erroneous count if the expected target does not exist. To check that measurement on the red target is being effected an output is taken from device 38 to a cathode follower to afford a radial line on the P.P.I. from the centre to the target, Figs. 5A and 7 (neither shown). The time measurement output is digital and is applied to a digital-to-analogue converter. Switching arrangements may be used whereby the complete apparatus includes two converters or one converter shared for red and green target range measurement output to the course recorder, Figs. 8-10 (none shown). Course recording, Figs. 12, 13, 14, 15. Arms 170, 171 are arranged one above the other over map 172. Each arm end 173 is pivotally supported by a bracket 174 and an annular bearing 175 on a triangular foot 176 having a support 177 formed from a magnet to hold 'the foot on the metal map table at the desired point, positioning at which is assisted by aperture 179. Arm end 180 is movably supported on the table by ball 181 in the lower end of levelling screw 182. Bar 183 of each arm has bevelled edges supporting a slide 185 comprising upper and lower plates 186 bolted together. Blocks 187, 188 are each provided with two sets of rollers 189 and block 187 is slidably disposed between the plates for adjusting the load applied on the rollers by screw 191. Aperture 194 is provided through the plates to receive a tube 195 interconnecting the slides and carrying pen 195a. The potentiometer 146 and servomotor 156 of each ranging registration are mounted on the end of a plotter arm and the motor drives a grooved drum carrying a wire 199a which passes over a laterally-adjustable idler pulley on arm end 180, Fig. 13A (not 'shown), and the wire is secured to slide 185 by connectors 199f. A prescribed course may be marked on the map and the operator checks deviation therefrom by viewing through hollow connector 195. Averaging measurements. For summing 10N travel times, N decade units are added in cascade to the time interval meter and the analogue converter includes voltage dividing networks, Fig. 17 (not shown). Target identification. The reflecting target may be associated with an adjacent aerial transmitting a continuous wave or random pulses on a frequency differing from that of the radar transmission, and the radar receiver is arranged to receive only those signals of frequency equal to the sum or difference of the radar and target-transmitter frequencies, Fig. 19 (not shown). Alternatively the radar transmissions are vertically polarized and the reflecting surfaces are formed to reflect only signals so polarized. Automatic azimuth selection. Each plotting arm turning movement is followed by a gear secured to a synchro-transmitter shaft and an associated receiver has its output shaft geared to the adjusting knob of the corresponding azimuth selector, Fig. 20 (not shown). Modifications. To allow for inaccuracy in azimuthselection it may be necessary to permit range measurement over an arc wider than the radar aerial beam width and this is accomplished by energizing the time measuring means resetting generator (52, Fig. 4) from the range control device (40, Fig. 5), Fig. 21 (not shown).